Hall of Primitive Mammals

Can you see the two puncture wounds in the top of this Glyptotherium skull? The bite probably killed the glyptodont. A large predator seized it from the front, either to knock it over or to immobilize it so other predators could attack. This species is the earliest glyptodont to appear in North America. Originating in South America, it reached Arizona and Texas shortly after the Isthmus of Panama was formed.

Panochthus was a giant glyptodont that lived in South America just before the extinction of the glyptodonts, at the end of the last Ice Age. The head of most glyptodonts was armored, and could also be retracted into the shell opening; the feet and tail were protected by armor as well. These shields deterred all but the most powerful carnivores from attacking this animal fortress.

These little armadillos are widely distributed in South America east of the Andes. They dig to obtain food (mainly plants and insects) and to create the burrows in which they live. The earliest known armadillos lived about 60 million years ago, primarily in South America. Few of their fossils have been found. Like this living relative, the early armadillos had flexible bands of armor spanning their bodies.

Achieving heights of 15 feet and weighing anywhere between two and four tons, Lestodon armatus was truly a dominating figure during the Pleistocene era. Observing its flaring muzzle, teeth, and trailing tail, it is not hard to picture this corpulent herbivore ranging through forests and feeding on the low grasses of the pampas, rising to its hind legs to browse leaves from higher trees.

Lestodon was an armored mammal—not dissimilar to the modern-day armadillo—with large bony plates embedded in its skin. Although these bony plates do not appear on the model, paleontologists have found preserved fragments of sloth skin with small pieces of bone lining their inner surface. Such giant sloths were found in South America as recently as 10,000 years ago; this formidable specimen was collected by J. Brachet in Buenos Aires, Argentina in the 1850s.

Mammals and Their Extinct Relatives

The diversity of mammals is truly astonishing. They have evolved to inhabit land, sea, and air and include eaters of plants, animals, and insects. As the centerpiece of the Hall of Primitive Mammals, this display pays tribute to the remarkable diversity of Mammalia by featuring fossil mounts of eight different species of mammals. Fittingly, these specimens have been collected around the world, from Los Angeles to Buenos Aries, from Mongolia to Madagascar.

This display—“Mammal Island”—demonstrates to visitors of all ages the inter-connectedness and diversity of life on Earth. Each animal featured represents an important branch of the mammal tree, including a primate and a marsupial, a proboscidean from the elephant family, an armored edentate, a lizard-like early synapsid, as well as the carnivorous saber-toothed cat. When viewed together, as in this innovative display, the variation in mammals is singularly impressive.

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Close Relatives of Mammals

Each of the specimens in this display reflects a fascinating point in the history of evolution. Paleontologists have discovered a sequence of fossil animals that lived between 250 and 200 million years ago each of which contributed a particular aspect to the development of mammals. This grouping examines those aspects, from the mammal-like stance of the Lycaenops ornatus to the dental adaptations of the dicynodonts.

These adaptations represent revolutionary changes in form that paved the way for the development of all mammals on Earth. By grouping these specimens together, paleontologists reveal these crucial evolutionary milestones and broader sweep of evolutionary history. The five specimens in this display were each collected in South Africa between 1913 and 1952. Of the five, three are complete skeletons.

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Dimetrodon limbatus
(di-ME-tro-don lim-BA-tus) “two shapes of tooth”

Predating dinosaurs by about 40 million years, Dimetrodon lived during the Permian age, an astounding 280 million years ago. It was most likely a top predator, feeding on fish as well as reptiles and amphibians. This full Dimetrodon skeleton was recovered from Godlin Creek, Texas in 1906 by noted paleontologist Ermine Cowles Case.

The purpose of Dimetrodon’s large sail remains a matter of debate, with some paleontologists arguing that the sail served anatomical purposes, while others assert that the sail was used to attract mates. Notably, this unique reptile evolved other key features that ultimately link it with contemporary mammals. With specialized bones in its lower jaw and the indication of an eardrum, the Dimetrodon bridges the evolutionary gap between reptiles and mammals. It is an inspiring figure—one that hints at the sometimes subtle interconnection of all life on Earth.

Distant Relatives of Mammals

The three complete skeletons in this display represent some of the earliest fossil specimens in the Museum. Uncovered across Texas and Oklahoma, these individuals originated in the Permian era, roughly 270 million year ago. Each of the reptiles in this display boast a specific body type and intriguing set of evolutionary adaptations that make them a unique and often mystifying group.

From the 12-foot, 800-pound Cotylorhynchus romeri to Edaphosaurus boanerges with its large spinal fin and tiny head, these distant relatives of mammals continue to inspire new theories and provoke discussions among paleontologists about the evolution and eventual rise of mammals. As this dialogue continues, the questions this group poses and the secrets they hold will no doubt broaden our understanding of our own evolutionary origins.